This invention relates to piezoelectric ink jet modules.
A piezoelectric ink jet module includes a module body, a piezoelectric element, and an electrical connection element for driving the piezoelectric element. The module body, usually carbon or ceramic, is typically a thin, rectangular member into the surfaces of which are machined a series of ink reservoirs that serve as pumping chambers for ink. The piezoelectric element is disposed over the surface of the jet body to cover the pumping chambers and position the piezoelectric material in a manner to pressurize the ink in the pumping chambers to effect jetting.
In a typical shear mode piezoelectric ink jet module, a single, monolithic piezoelectric element covers the pumping chambers to provide not only the ink pressurizing function but also to seal the pumping chambers against ink leakage. The electrical connection is typically made by a flex print positioned over the exterior surface of the piezoelectric element and provided with electrical contacts at locations corresponding to the locations of the pumping chambers. An example of a piezoelectric shear mode ink jet head is described in U.S. Pat. No. 5,640,184, the entire contents of which is incorporated herein by reference.
In one known ink jet module, available from Brother, a resin diaphragm is provided next to each of the pumping chambers. The central region of each diaphragm is pumped by a piezoelectric feature. Electrodes are embedded in the piezoelectric material.
This invention relates to a piezoelectric ink jet head that includes a polymer, preferably a flex print, located between the piezoelectric element and the pumping chambers in the jet body. The polymer seals the pumping chambers and also positions the electrodes on the side of the piezoelectric element in which motion is effected, which can reduce the magnitude of the drive voltage required for operation. The compliant flex print material also can provide electrical, mechanical, and fluidic pressure isolation between pumping chambers, which improves jetting accuracy.
Thus, in one aspect, the invention features a piezoelectric element that is positioned to subject the ink within an ink reservoir to jetting pressure. A flexible material carries electrical contacts arranged for activation of said piezoelectric element and is positioned between the reservoir and the piezoelectric element in a manner to seal the reservoir.
Implementations of the invention may include one or more of the following features. The material may be a polymer. The ink reservoir may be defined by a multi-element module body. An ink fill flow path leading to the reservoir may be sealed by the polymer. The polymer may include an area that is not supported. The piezoelectric element may be sized to cover the reservoir without covering the ink fill flow path. The module may include a series of reservoirs all covered by a single piezoelectric element, or in other examples by separate respective piezoelectric elements. The module may be a shear mode piezoelectric module. The piezoelectric element may be a monolithic piezoelectric member.
In other general aspects of the invention, the flexible material over the flow path contains an area that is not supported; the piezoelectric element spans the ink reservoir and is positioned to subject the ink within the reservoir to jetting pressure; and electrical contacts are located only on a side of the piezoelectric element adjacent to the ink reservoir. In some implementations, the contacts may be thinner than 25 microns, preferably thinner than 10 microns.
Other features and advantages will become apparent from the following description and from the claims.